A Panhard 24 ? :)

Hi Jean-Paul, do you have an example model of a sweep that you found frustrating that you could post?

It's always helpful for me to see actual model examples rather than just some text description.

But Sweep does tend to have more numerous "forces" applied simultaneously, which can sometimes tend to make for problems. Using fewer profiles and trying to avoid forcing a single surface through too many changes in shape can help to make a more relaxed surface in general.

- Michael

Hi Michael,

Actually, I think you described the matter very well. Maybe “frustrating” is not the right word. In the beginning, I used to draw as many profiles as I could from the body plan of a ship or airplane and sweep (or loft) through them. It often produced suboptimal surfaces, with kinks and unwanted bumps etc. I learned that way that it pays to make the original curves as simple and smooth as possible. But event so, I got a bit frustrated with the method, for example when mirroring a half fuselage made by Sweep only to find a gap of a kink at the edges, something that was not apparent with a seemingly satisfactory surface. Probably, cleaning up the curves would pay handsome dividends but even so…

Anyhow, it appeared that suing less profiles and generating the entire fuselage rather than half of it would help. That is when I started using Network and Blend more and more, to the point that I rarely use Sweep for generating large body elements. You know that I put great store on continuity and I feel that I can ensure more of that this way.

I do not imply that Sweep does not work well, just that there are better ways of achieving the kind of output that I am after. I love the way Blend works, and I wish you would expand that area of MoI to give the user (me!) more control and options, and more generally strengthening even more an already strong point of the software, such as the ability to blend several edges and control bulge on each side the way Rhino does etc.

Hi Jean-Paul, probably the area of Sweep that you don't like is the "morphing" aspect of the profiles.

For Sweep, areas between profiles get a kind of blend between each profile curve, with a kind of "ease in/ease out" type stepping mechanism.

That blending method is like this:




You can see that kind of weighted blending in a sweep:






That kind of proflie to profile blending is pretty much the standard way that it is done - you'll see that same thing happen in Rhino for example.

One thing you can do to reduce it from being a factor is to also use a scaling rail, which will then kind of override the profile shaping. So for example:






Maybe in the future I'll be able to change the way the profiles are blended together to avoid that kind of stepping effect, I have some ideas. But it will probably involve re-writing some pieces of the geometry library sweep mechanism.

- Michael

Michael,

I see. Very enlightening!

But I seem to get just the same result with Network, which I understand to be a sort of Sweep in two directions simultaneously. With the advantage of being able to add more than just one rail in order to better control the output.

On the topic of what I find frustrating and might like better/smarter tools, there is the curve rebuild function. To help ensure smooth surfaces, it pays to have "perfect" curves. I have taken the habit of generating curves with liberal use of the Blend tool and to otherwise rebuild curves. I never know how many points to ask for that would simplify/smooth/fair the curve while preserving the general shape of the original sketchy curve. A sort of clever interpolation that would minimize deviation from the original curve with the least possible number of points to sooth out the shape would be more than nice to have. Or is it there already somewhere and I simply missed it so far?

Hi Jean-Paul,

> But I seem to get just the same result with Network, which I
> understand to be a sort of Sweep in two directions simultaneously.

It's more like _Loft_ in two directions simultaneously.

So yes, it does give more the kind of shape that I showed there with that particular sweep + scaling rail example.

For example a Loft where you don't use any rails looks like this:






Sweep works more by actually sliding the profiles along the rails, while simultaneously morphing them between different profiles shapes. If you are having things going around a bend, Sweep kind of maintains a more rigid shape as it goes around the bend, see this previous example:
http://moi3d.com/forum/index.php?webtag=MOI&msg=3081.23


Re: Rebuild - are you using the older "RebuildCurve" command that Petr posted, or the new "Rebuild" command that in the latest beta?

In the new one there are 2 different modes, a "Rebuild to tolerance" mode, and a "Rebuild by # of points" mode:



If you use "Rebuild to tolerance" mode, it will use as many points as needed in the rebuilt curve to get it within the distance that you enter from the original curve.

If you don't want to worry about exactly how many points to use, then try using that tolerance-based rebuild mode.

- Michael

Michael,

Once again, uh-um ! I had missed that new Rebuild thing completely. I will try it ASAP, but it seems to be pretty much what I had in mind.

Tanks again for taking the time.

Jean-Paul